Untested! 51mm × 51mm board, for isolating up to 8 buttons or switches, using only through-hole components. Switches are connected between SWn and SWGND. There are pads for eight 100nF (0.1uF) debouncing capacitors. The current to each optoisolator is roughly 5mA. The isolated DC-DC converter provides approximately 150mA to +4.5V. Components have been chosen for easy ordering from LCSC.com. Multiple boards can be used in parallel, with their SW#, SWGND, and +4.5V lines connected. This allows the same buttons to provide signals to e.g. multiple microcontrollers. When multiple boards are connected in parallel, the diodes ensure the DC-DC converters are not backfed. The 250 Ohm resistor ensures the converter output is loaded by 20mA at all times. For use with USB-connected microcontrollers using 3.3V signal levels, like Teensy LC/3.0/3.1/3.5/3.6, connect +5VIN to VUSB, OVCC to 3.3V, OGND to GND, and SW1 through SW8 to suitable input pins.